The present invention relates to mounting or support installations providing a base for a tripod-type structure which is vertically oriented during normal use, but which must periodically be moved to a substantially horizontal orientation. More particularly, the invention relates to an installation intended to support a runway approach lighting tower, or similar structure, for essentially unstressed pivotal movement between upright and horizontal positions.
In many modern airports the terrain is such that runway approach lights must be supported on towers a considerable distance above ground level. Conventional towers are normally tripod-type structures which may have a single light at the top, or a horizontal bar supporting a plurality of lights. In any case, since the optical axis of the light or lamp must be in a predetermined orientation with respect to the intended approach path of incoming aircraft, it is necessary that the individual lamps be precisely positioned upon the supporting structure.
The major structural components of conventional approach light towers are of lightweight, frangible aluminum tubing so that, in the event a tower is struck by an approaching aircraft, the tower will be sheared off before causing serious structural damage to the aircraft. Consequently, the towers are not strong enough to support a person climbing to the top whereby, in order to reposition the lamps, the tower must be lowered to make the lamps manually accessible and adjustable from ground level. In conventional installations this is presently accomplished by mounting two of the three tower legs for pivotal movement, temporarily detaching the third tower leg from its mounting, and rotating the tower about the pivotal mounting of the two legs. Due to the additional weight and possible torsional forces applied to the pivotally mounted legs as the tower is lowered and raised, structural damage to the tower or misalignment problems may result.
It is a principal object of the present invention to provide a novel and improved base support installation for a tripod structure which must be moved about a horizontal axis at or near the tripod base.
A further object is to provide a pivotable support structure for a runway approach lighting tower which reduces the stress on tower structural components during movement between vertical and horizontal orientations.
Other objects will in part be obvious and will in part appear hereinafter.